1. Field of the Invention
The present invention relates generally to a vibration insulator for use in automotive vehicles and the like and more specifically to an insulator which damps vibration by pumping a working fluid from one chamber to another through a flow resistance.
2. Description of the Prior Art
FIGS. 1 and 2 of the drawings show an insulator arrangement disclosed in Japanese Patent Provisional Publication No. 48-35151(1973) (based on U.S. patent application Ser. No. 755,268 filed on Aug. 26, 1968 now U.S. Pat. No. 4,595,867. This arrangement comprises two co-axially arranged tubular members 1, 2 which are interconnected by an elastomeric body 4 disposed therebetween and fixedly secured thereto.
A plurality (two) of recesses 6, 6 are formed in the outer periphery of the elastomeric body 4. These recess are closed by the outer tubular member 2 in a manner to define chambers 8, 8 which are filled with an incompressible working fluid.
A generally diametrically disposed straight channel defines a passage 10 which is formed through the elastomeric body per se in a manner to establish fluid communication between the chambers 8, 8. As shown in FIG. 2 this passage 10 is relatively small in diameter with respect to the inner tubular member 1.
With this construction when the outer tubular member 2 (for example) is subject to vibration the relative motion between the inner and outer tubular members 1, 2 in a direction normal to the axes thereof distorts the elastomeric body 4 in a manner which causes fluid to be to pumped from one chamber to the other via passage 10.
This arrangement while being simple in structure and relatively easy to produce, has suffered from the drawbacks that as the passage 10 which interconnects the chambers extends directly from one chamber to the other in a generally diametrical fashion through the elastomeric body 4, the length of passage 10 tends to be relatively short. This results in a limited vibration damping capacity. Further, due to the formation of the passage 10 in the elastomeric body 4 it is difficult to control the dimensions of the passage during mass production within desired limits.
Another problem comes in that during operation, as the passage 10 is defined in the elastomeric body 4 per se, the flow of working fluid through the passage tends to errode the walls thereof relatively quickly thus reducing the working life of the unit.